The killing is the second beheading of an American journalist in two weeks, and the militant group said it's a result of Obama's decision to conduct airstrikes against ISIS in Iraq.

Sotloff was also an Israeli citizen, a spokesman for the Israeli Ministry of Foreign Affairs said Wednesday.

In the video, Sotloff kneels in the desert, dressed in an orange prison-style jumpsuit. A masked "executioner" lords over him, wielding a knife.

U.S. Secretary of State John Kerry said the latest video shows ISIS' "unfathomable brutality."

"For so many who worked so long to bring Steven and the other Americans home safely, this was not how the story should've ended," he said in a statement Wednesday.

"It's a punch to the gut. The U.S. government has used every military, diplomatic and intelligence tool we have, and we always will. Our special operations forces bravely risked a military operation to save these lives, and we've reached out diplomatically to everyone and anyone who might be able to help. That effort continues, and our prayers remain -- as they always are -- with the families of all hostages who remain trapped in Syria today."

This summer, several dozen of the most elite U.S. commandos flew into Syria but couldn't find the hostages, including Sotloff and fellow journalist James Foley, a U.S. official told CNN last month.

The video of Sotloff's execution is similar to one released two weeks ago showing Foley's killing.

The journalist speaks; the executioner speaks. Then the victim is beheaded.

In the video released Tuesday, a British hostage is shown after the beheading of Sotloff, just as Sotloff was shown in Foley's video.

Obama said the United States "will not be intimidated" by the killers.

"Those who make the mistake of harming Americans will learn that we will not forget ... that our reach is long and that justice will be served," the President said.

He addressed his much criticized statement last week that he has no strategy on ISIS. He said he was referring to a military strategy in Syria that "might" require congressional approval.

"Our objective is clear. That is to degrade and destroy (ISIS) so it's no longer a threat," he said. "We can accomplish that. It's going to take some time, it's going to take some effort."

ISIS, or the Islamic State in Iraq and Syria, refers to itself as the "Islamic State."

Obama said the world needs a regional strategy to defeat the group.

"We've been putting together a strategy that was designed to do a number of things. ... What we have to make sure is we have a regional strategy in place," he said.

In addition to the Americans' deaths, the British hostage showed at the end of the latest video appears to be in danger.

The UK said it attempted to rescue its citizen "some time ago" but failed.

UK Foreign Secretary Philip Hammond provided scant details of the rescue attempt or any other plans in the works.

"You wouldn't expect me to discuss various options that we will be considering," he said. "But I can assure you that we will look at every possible option to protect this person."

Britain echoed the same sentiment as Obama.

"This country will never give into terrorism ... a country like ours will not be cowed by these barbaric killers," UK Prime Minister David Cameron said.

"Our thoughts are with the British hostage and his family," Cameron said Wednesday in the House of Commons.

The video

The video of Sotloff's killing has eerie similarities to the one released by ISIS last month of Foley's execution.

"It is almost the exact same choreography," said Peter Neumann, a professor at King's College London.

The executioner appears to be the same person, and the location of the two killings also appears to be similar. Neumann suspects they took place in or around the Syrian city of Raqqa, one of the safest areas for ISIS.

'I'm back, Obama'

Sotloff's executioner speaks in what sounds like the same British accent as the man who purportedly killed Foley.

He's dressed identically in both videos, head to toe in black, with a face mask and combat boots. He appears to be of similar build and height. He waves a knife in his left hand, as did the militant in the video of Foley's death.

And then, there are his actual words.

"I'm back, Obama, and I'm back because of your arrogant

foreign policy towards the Islamic State," the executioner says in the second video. "Just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."

The SITE Intelligence group says there's no question the same masked fighter appears in both videos.

After Foley's death, the British ambassador to the United States said that experts in his country were close to identifying the killer. He has not yet been named.

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